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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Record number 496742
Title Bubble coalescence : Effect of bubble approach velocity and liquid viscosity
Author(s) Orvalho, Sandra; Ruzicka, Marek C.; Olivieri, Giuseppe; Marzocchella, Antonio
Source Chemical Engineering Science 134 (2015). - ISSN 0009-2509 - p. 205 - 216.
Department(s) Bioprocess Engineering
Publication type Refereed Article in a scientific journal
Publication year 2015
Keyword(s) Bubble approach velocity - Bubble coalescence - Liquid viscosity - Transition regime

The goal of this study is to present new experimental data on the effect of the bubble approach velocity and liquid viscosity on pairwise bubble coalescence. Measurements were performed to investigate the dynamics of bubble coalescence under well-defined laboratory conditions. Air and pure aqueous solutions of alginate (no surfactants) were the phases. The bubbles were formed from two vertical capillaries, under constant flow conditions. The coalescence process was recorded with a fast video and then image analysed, to evaluate the bubble growth, bubble expansion rate, the first bubble touch, bubble contact time T, bubble coalescence efficiency E. Three control parameters were tested. The bubble size D on contact was set by the spacing between the capillaries (D=1 and 1.5mm). The bubble approach velocity V was controlled by the gas input (V=0.031-39mm/s). The liquid viscosity μ was adjusted by the alginate content (μ=1.2-10.3mPas). It was found that the bubble contact time T monotonously increases with the liquid viscosity, passing through three stages: initial rise (low μ, coalescence), then jump (intermediate μ, transient region), and finally forming a plateau (high μ, non-coalescence). In the coalescent regime, the bubble contact time monotonously decreases with the bubble approach velocity obeying a power law, which for a typical 1mm bubble reads: T~V-0.85. The difference in the bubble size did not change the coalescence pattern qualitatively, but only quantitatively in a modest manner.

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